Hard disk drives are used in almost all computer system operations. In fact, most computing systems are not operational without some type of hard disk drive to store the most basic computing information such as the boot operation, the operating system, the applications, and the like. In general, the hard disk drive is a device which may or may not be removable, but without which the computing system will generally not operate.
The basic hard disk drive model was established approximately 40 years ago and resembles a phonograph. That is, the hard drive model includes a plurality of storage disks or hard disks vertically aligned about a central core that spin at a standard rotational speed. A plurality of magnetic read/write transducer heads, for example, one head per surface of a disk, is mounted on the actuator arm. The actuator arm is utilized to reach out over the disk to or from a location on the disk where information is stored. The complete assembly, e.g., the arm and head, is known as a head gimbal assembly (HGA).
In operation, the pluralities of hard disks are rotated at a set speed via a spindle motor assembly having a central drive hub. Additionally, there are channels or tracks evenly spaced at known intervals across the disks. When a request for a read of a specific portion or track is received, the hard disk drive aligns a head, via the arm, over the specific track location and the head reads the information from the disk. In the same manner, when a request for a write of a specific portion or track is received, the hard disk drive aligns a head, via the arm, over the specific track location and the head writes the information to the disk.
Over the years, refinements of the disk and the head have provided great reductions in the size of the hard disk drive. For example, the original hard disk drive had a disk diameter of 24 inches. Modern hard disk drives are generally much smaller and include disk diameters of less than 2.5 inches (micro drives are significantly smaller than that). Refinements also include the use of smaller components and laser advances within the head portion. That is, by reducing the read/write tolerances of the head portion, the tracks on the disk can be reduced in size by the same margin. Thus, as modem laser and other micro recognition technology are applied to the head, the track size on the disk can be further compressed.
A second refinement to the hard disk drive is the increased efficiency and reduced size of the spindle motor spinning the disk. That is, as technology has reduced motor size and power draw for small motors, the mechanical portion of the hard disk drive can be reduced and additional revolutions per minute (RPM) can be achieved. For example, it is not uncommon for a hard disk drive to reach speeds of 15,000 RPM. This second refinement provides weight and size reductions to the hard disk drive and increases the linear density of information per track. Increased rates of revolution also provide a faster read and write rate for the disk and decrease the latency, or time required for a data area to become located beneath a head, thereby providing increased speed for accessing data. The increase in data acquisition speed due to the increased RPM of the disk drive and the more efficient read/write head portion provide modem computers with hard disk speed and storage capabilities that are continually increasing.
Particularly, with regard to data storage devices, these advances have attributed to increases in storage density. However, the increase in storage density has led to weaker and/or smaller signal strength emitted by each data bit. This has required the development of read/write heads having increased sensitivity to the intensity of the signals emitted by the data bits. Increased sensitivity needs require improved testing techniques to ensure proper and precise functioning of the read/write head.
Specifically, within the read/write head fabrication and assembly process, there are general processes that are performed on the read/write head prior to the read/write head being mounted into the hard disc drive assembly. Prior art FIG. 1A is an exemplary flowchart 10 of a process for fabrication and testing of a read/write during certain stages of the fabrication process.
Step 11 is the wafer fabrication. This step is where the components of the read/write head are created. Examples of some of the components that may be implemented in a read/write head fabricated on the wafer may include a magnetic shield layer(s), the pinned layer, the conductive spacer layer, the free layer (sensor), the contact layer, the writer layer, and additional layers and/or components. There may be thousands of read/write heads fabricated on a single wafer.
Subsequent to completing wafer fabrication 11, the process continues to step 12, slider fabrication 12. Slider fabrication 12 is a process for cutting the wafers into thousands of individual sliders where each slider has a reader and a write element and a proper air-bearing surface on one side of the slider. Slider fabrication can include slicing the read/write head from the wafer, lapping each slider to achieve a proper reader strip height and resistance, are on design target, and to define the air-bearing surface. Slider fabrication can also include depositing a protective overcoat for protection against corrosion and head disk interface robustness.
Subsequent to the lapping process in slider fabrication 12, the process proceeds to step 13, a quasi-static test (QST). QST 13 is for testing reader signal amplitude (sensor sensitivity), reader asymmetry (similar peak to peak readings for a waveform) and reader instability. QST 13 has several shortcomings, one of which is while QST 13 is a functional test it is not a direct test. For example, the slider is placed into conventional magnetic field, referred to as a uniform field. This uniformity does not replicate the field emitted from a platter (disc) as the disc emits small local fields. The measurement can also be affected by changes in reader shield shapes and properties.
A further shortcoming to QST 13 using a uniform field is that QST 13 does not test the read/write head for recession, protrusion, or other deformity. If the read/write head has recessions, the reader is not disposed on the edge of the air-bearing surface (ABS). Because of the applied uniform field, the transducer is not effectively screened. If the read/write head is not disposed at the ABS, the read/write head will not function properly when applied to a disc where each bit region may emit varying charge states. A uniform field only determines if the head can sense, not the sensing accuracy of the read/write head
Another shortcoming to QST 13 is matching the characteristics of the local small fields emitted from a disc. To enable this, an offset is provided in case of change in design of a shield. The shield is a structure that isolates the reader from adjacent bit fields, thus providing better resolution. When the reader reads from one bit space, the reader is not influenced by an adjacent bit region. However, the shield provides an extra field during QST 13. Thus, when the data relative to the extra field in the shield is accessed, a correction factor is needed. Further, when the reader or shield design changes or an alternatively designed reader is subject to QST 13, the correction factors required modifications. While QST 13 can return favorable numbers within the static test, QST 13 does not adequately address reader value quality and/or real performance, and the results vary upon fabrication inconsistencies and design changes. For example, if QST 13 gives a number 10 (acceptable for one design) and then gives the number 10 for another design, this number may not be correct because of the shielding characteristics. QST 13 requires adjustment to obtain the real value, and the value varies from configuration to configuration. The value is not uniform nor is the value universally applicable. If the read/write head fails QST 13, the read/write head is rejected, e.g., sent to disposal 20.
However, upon the read/write head passing QST 13, the read/write head slider is then sent to step 14, head gimble assembly process (HGA) 14. In HGA 14, the read/write head slider is mounted to an entire assembly, the head gimble assembly. The HGA includes the slider and the suspension, the flex component. The slider is commonly bonded to the suspension. The suspension has a spring-like quality, which causes the air-bearing surface of the read/write head slider to be placed against the platter to cause the slider to fly at a precise distance from the platter.
Once the HGA is completed in step 14, the process proceeds to step 15, a dynamic electrical test (DET) 15, also referred to as a magnetic dynamic test (MDT). DET 15 has been implemented for testing read/write head performance as a QST 13 does not test for characteristical deficiencies in the read/write head slider. DET 15 tests an entire HGA assembly.
Digressing from flowchart 10, FIG. 1B shows an exemplary test machine 30 for performing DET 15 of FIG. 1A. It is common for a test machine 30 to cost upwards of a quarter of a million dollars (US) per machine. Further, it is not uncommon for companies making hard disk drives to have hundreds or thousands of test machines 30 for performing a DET 15. Shown in FIG. 1B are HGA 25 and mounted slider 26. HGA 25 is removably mounted to a device 34. Device 34 is for orienting HGA 25 upon the magnetic data layer of platter 50. Device 34 can move HGA 25 as indicated by arrow 33. FIG. 1B also includes device 31 for rotating a platter 50. Device 31 can rotate platter 50 as indicated by arrow 51. Device 31 rotates platter 50 at a speed equivalent to the rotational speed of the platters in the hard disc drive into which HGA 25 is to be placed. Also shown is a data collector 32 that collects data acquired from devices 31, platter 50, and device 34 during performance of DET 15. DET 15 is fully capable of detecting most characteristical deficiencies and physical problems that may be present in slider 26 and/or HGA 25.
However, DET 15 has some shortcomings. One shortcoming is the cost of DET 15 is non-trivial. Costs can include, but which are certainly not limited to, assembly of an HGA 25 (slider on suspension), placing the HGA into a cartridge for mounting to the expensive testing machinery, labor costs for performing the test, clean room real estate allocated for the testing machinery, cost of the machinery, etc.
Referring back to FIG. 1A, specifically step DET 15 of process 10, when a reader component, e.g., read/write head slider 26 of HGA 25, tests to have acceptable reader characteristics, process 10 proceeds to step 16, a head assembly process. If a read/write head fails DET 15, the entire HGA 25 assembly is then rejected, e.g., disposal 20. Continuing, process 10 then proceeds to step 17, a drive assembly process. Then process 10 proceeds to a final test 18, and if the assembly passes, on to step 19, the delivery of completed hard drives.
However, if the reader (transducer) component of HGA 25, e.g., read/write head slider 26, tests such that the characteristics of the reader according to DET 13 are unsatisfactory, the entire HGA 25 is discarded, e.g., disposal 20. It is noted that discarding an HGA 25 is a non-trivial cost.